I have an Arduino with a 433mhz receiver attached. I've connected this to my computer via a usb to serial cable.
Connected to my laptop (development machine) it works fine with it (>15 metres), but when connecting it to the Raspberry pi (deployment machine) via the same USB cable the range is REALLY poor (<1 metre).
I've tried using another laptop and again it works fine. Suggesting something is wrong/different going on with the Raspberry Pi.
I measured the voltage at the 433mhz receiver and it was slightly lower when it was connected to the raspberry pi. I tried to rule this add by adding a voltage booster circuit but it made it worst if anything.
laptop = 4.88v
raspberry pi = 4.3v
raspberry pi using booster circuit = 4.98v
I've not tried an external power supply yet.
Any thoughts on what might be causing the problem?
I connected up an external power supply to the receiver instead of using the power coming from the Raspberry Pi / Arduino. This made an amazing difference to the range.
For the receiver module I was working with 5.5V - 6V seemed to give the best range. Anything below 5V was pathetic.